1. Field of the Invention
This invention relates to reserve type primary galvanic batteries. In particular, it relates to reserve batteries which operate by immersion in seawater.
2. Description of the Prior Art
There is a class of batteries employing zinc, aluminum or magnesium anodes and silver chloride, copper chloride other halides of copper or lead chloride cathodes which are activated by and operate submerged in a weak aqueous electrolyte such as seawater.
As a generality, it has been found that for reasonable galvanic battery operation each cell of a battery should have its own electrolyte and that the electrolyte of one cell should not be linked to the electrolyte of another cell. If there are electrolyte bridges from cell to cell, a leakage current will flow through the electrolyte bridge. The leakage current represents a non-productive drain on the battery and results in reduced battery output and life. However, in the present instance, the resistivity of the electrolyte is so great that an electrolyte common to all cells may be used without overriding problems related to the short circuiting of the battery by the common electrolyte.
When immersion type batteries are used for relatively short discharges lasting from 1/4 hr. or less, the leakage currents are usually so minor that the battery can be made completely open to the electrolyte. However, for longer discharge rates and in order to obtain maximum useful work from the battery, it has been found desirable to minimize the leakage currents by providing constrictions in the electrolyte feed passages. When this is done, another factor enters the picture. Reaction products formed as a result of the battery discharge collect in the feed passages and can seriously interfere with the behavior of the battery. The purposes for which seawater batteries are used require that the battery becomes operable in as short a time as possible. The time required for a battery to build up to operating voltage after immersion is often known as the "rise time" or activation time of the battery. In generalities, a battery to be used for a short discharge rate is expected to have a short rise time whereas the rise time of a battery that must operate over a long time period is usually expected to be longer. The shape, length and area of the feed ducts all have an effect on the rise time of a seawater battery. The more narrow and tortuous the feed ducts the longer it will take for the battery to fill and the slower will be the rise time.
Many investigators have worked to determine the best configuration for the electrolyte feed channels for use in water activated batteries for particular applications.
Batteries have been designed having long individual pipes for entrance and exit of electrolyte. Batteries have been designed with internal spaces in which the residual materials may collect without harm.
In certain electrical devices, it has been found expedient to "ground" the frame or to have one common uninsulated conductor, often having considerable exposed metal surface. When such a device is used with an ordinary seawater battery in a total immersion mode, the leakage currents are found to be considerably greater than when the device is constructed without the grounded frame. The grounded frame may be connected to the positive or the negative of the battery depending upon the electrical circuit used.
An annoying feature of some seawater batteries is that they have a fluctuating output voltage. The fluctuations may be perhaps 0.5% of the output voltage, they may occur quite rapidly. When used with accoustive devices, the voltage fluctuations result in a background "noise" that reduces the sensitivity of the device.
Batteries of the type suitable for use with the present invention are used at moderage depths below the surface of the water -- say down to 50 or 60 ft. They may also be required to operate at considerably greater depths, up to several thousand feet. The static pressures on the battery and other equipment are correspondingly great. It has been found that the leakage currents under high pressure conditions are greater than the leakage current at near surface pressures.